Simple case hardening recipe

[choochoo_balooParticipant @choochoo_baloo]

[choochoo_balooParticipant @choochoo_baloo]

Dear all,

I want to attempt to case harden a mild steel screwdriver I have made. Any advice on what I should use as a case hardening mixture? I have already ground up charcoal briquettes in to a powder. I've not found any consistent recommendations if any extra additives eg. salt presumably for the sodium

After youtube research, I plan to:

1. Heat steel to cherry red
2. Immerse in mixture and leave for say 5 mins
3. Knock off crust and reheat to cherry red before water quenching

Sound ok? Thank you in advance.

Edited By choochoo_baloo on 27/03/2023 17:35:56

[DMBParticipant @dmb]

Sounds very similar to schoolday metalwork class method. We used a commercially produced jollop, – "Kasenit" ?? Too long ago to be any more precise – we had Radio Caroline playing in workshop with The Animals singing "House of the Rising Sun".

[GeorgineerParticipant @georgineer]

I've read that Kasenit is no longer available. My great-grandfather (an "Engine Smith" ) used a mixture of hoof clippings and leather offcuts…

George

Edited By Georgineer on 27/03/2023 17:57:45

[choochoo_balooParticipant @choochoo_baloo]

Yeah Kasenit was discontinued a while ago apparently. Can either of you provide details? (As much as I enjoy the anecdotes!)

[duncan webster 1Participant @duncanwebster1]

Endless case hardening powder available on ebay

[JasonBModerator @jasonb]

I use the Beta compound from EKP also widely available elsewhere.

Will case hardening be enough for a scewdriver? More usual to use a carbon steel and through harden so the blade does not twist on the first tight screw you come across

[Grindstone CowboyParticipant @grindstonecowboy]

+1 on what Jason said, don't ask me how I know…

Although it's a learning experience, I guess.

Rob

[BazyleParticipant @bazyle]

The OP's original method won't work apart from what was said about overall strength of the core. The heat/dip/ process works with kasenit because it contains a cyanide derivative which decomposes to release active carbon that quickly penetrates the surface.
The traditional methods rely on plain carbon (charcoal) being in contact for a long time. This also runs the risk of burning off both the iron and the carbon so again traditionally methods were needed to prevent this. So items are put in a tin/iron pot /container that can be sort of sealed. Then calcium carbonate was added to the charcoal in the form of lime if available or bone which was typically also knocking around the blacksmiths, to decompose giving off CO2 which expelled the air before it was hot enough to burn any of the iron causing pitting or marking of the item. use of leather offcuts was just a mixture of folklore and deliberately making it seem like a 'special' process.

[Mike PooleParticipant @mikepoole82104]

Silver steel is a readily available high carbon steel and a reasonable screwdriver can be made from it. Heat treatment is straightforward, heat to red heat and quench in water, clean and polish and heat gently to temper to the colour required, blue is usually suitable for a screwdriver. Case hardening will give a hard wearing surface but the core will not be the tough steel needed for a screwdriver. If the intended use is for light duty assembly work rather than some heavy duty screw driving then case hardened steel might be suitable.

Mike

[Robert ButlerParticipant @robertbutler92161]

Posted by choochoo_baloo on 27/03/2023 17:34:33:

Dear all,

I want to attempt to case harden a mild steel screwdriver I have made. Any advice on what I should use as a case hardening mixture? I have already ground up charcoal briquettes in to a powder. I've not found any consistent recommendations if any extra additives eg. salt presumably for the sodium

After youtube research, I plan to:

1. Heat steel to cherry red
2. Immerse in mixture and leave for say 5 mins
3. Knock off crust and reheat to cherry red before water quenching

Sound ok? Thank you in advance.

Who on earth would suggest making a screwdriver from mild steel and then case harden it?

Robert Butler

[Trevor Drabble 1Participant @trevordrabble1]

Blackgates also sell case hardening powder . They had it on the stand at Harrogate . Think it was around £17 / tub.

[Alan CharlestonParticipant @alancharleston78882]

Hi Choochoo,

You might find some useful comments here:

https://www.model-engineer.co.uk/forums/postings.asp?th=64390

Regards,

Alan

[SillyOldDufferModerator @sillyoldduffer]

Posted by choochoo_baloo on 27/03/2023 17:34:33:

Dear all,

I want to attempt to case harden a mild steel screwdriver…

To be pedantic, case-hardening is done in a case. The case is usually a steel container full of pure carbon, not coal, and maybe a few additives of the type found in Kasenit and such mixtures. The carbon is packed as desired around the whole item, or just one face, and then the case is sealed shut – air-tight.

Then the case is left in an oven at red-heat for several hours, maybe longer. Being sealed keeps air and other nastiness away from the diffusion, so results are more predictable. Being able to soak the item inside a sealed case means is the hard layer can be given time to develop much deeper into the metal, and its hardness can also be controlled in various useful ways altering the temperature as the item cooks. More precise and effective than simpler hardening methods if needed, but extra cost and fuss.

Dave

[duncan webster 1Participant @duncanwebster1]

To be equally pedantic, that's pack hardening. Any process that produces a hard skin and soft core is case hardening, and there are quite a few. When I were a lad heat treatment shops had vats of molten cyanide, it's a wonder anyone survived.

[Roderick JenkinsParticipant @roderickjenkins93242]

Quite right Duncan. I expect SOD to correct the record at the earliest opportunity

Rod

[SakuraParticipant @sakura]

Posted by duncan webster on 28/03/2023 19:52:12:

To be equally pedantic, that's pack hardening. Any process that produces a hard skin and soft core is case hardening, and there are quite a few. When I were a lad heat treatment shops had vats of molten cyanide, it's a wonder anyone survived.

When I worked in an engineering factory they used molten cyanide in the Hardening House. 2 of us maintenance fitters were sent to change the pot. Started to chip away at the grout around the top edge. A piece flew off right onto my tongue. I spent quite a time spitting! The new cyanide tablets lay all over the floor and the blacksmith proudly told us one tablet in the local water tower would be enough to kill the population of the local town! Elf and Safety! Actually, some things have improved for the better. (Ps, I didn't die!)

[bernard towersParticipant @bernardtowers37738]

Sorry to disagree but it’s called box hardening and brown paper is put in first

[Peter KroghParticipant @peterkrogh76576]

Well, I learned, blacksmithing, that an iron box with a snug lid ( didn't need to be super sealed) packed with leather trimmings with the object in the center and heated to a bright yellow and held there for a couple of hours would put a nice case, about .020" thick on flint lock parts very well. Learned the method 50 years ago from a very skilled gunsmith. Large parts would obviously need large equipment of which I am quite naked.

Have fun, try things!

Pete

[Bill Davies 2Participant @billdavies2]

We called it pack carburising, cast iron boxes filled with short charcoal sticks, similar in size to the charcoal used for drawing but perhaps 3/4" long. Multiple boxes heated in a large muffle furnace, left to cool overnight. Case hardening refers to the hardened 'case' around the softer, tougher core, after the part is reheated and quenched. I don't recall a tempering process but it's a number of decades ago.

Bill

[SillyOldDufferModerator @sillyoldduffer]

Posted by Roderick Jenkins on 28/03/2023 20:45:44:

Quite right Duncan. I expect SOD to correct the record at the earliest opportunity

Rod

I plead 'not guilty' this time!

My Oxford English Dictionary dates first use of 'case-harden' in print to 1677 (which date is repeated in the Wikipedia article). Though iron-workers didn't know it at the time, the surface was hardened by carburisation, i.e encouraging carbon to diffuse into an Iron surface by heating the two in contact at about 2000°C for quite a long time.

Furnace fires are filthy. Carburisation occurs along with a lot of other undesirable chemistry that makes results unpredictable. Therefore a case was used to protect the job and the chemicals from corruption.

The case could be clay, but cast-iron became popular (because it's cheap), Wrought iron was recommended because it lasted longer, and Nichrome is used for precision hardening.

The original mix was sliced leather (a source of clean carbon), and it was soon discovered adding horn made it work more reliably. The horn provided Nitrogen. This combination is still recommended one of my books dating to about 1930, though they suggest buying a commercially consistent bagful rather than making your own. By 1948, chemical mixtures are recommended: charcoal and Potassium Ferricyanide and/or Barium Carbonate. In 1948 Barium Carbonate was preferred, I don't know if that's still true.

Technology marches on. An actual protective case was essential when furnaces were no more sophisticated than a heap of dubious fuel and a bellows. When clean heat became available and the science was understood, the need for a separate protective case diminished – in effect the furnace is the case!

As the original 'case-hardening' slid towards meaning 'any skin hardening process', it became necessary to invent new terms to cover several hardening processes; for example 'Pack Hardening' is now used to describe the original process using a sealed box.

English constantly shifts, and mechanical engineering might be worse than most. The year I left school, they threw out their collection of old technology text-books, and we were allowed to take our pick. Interesting because what boys were taught in 1933, had changed markedly by 1945, 1954 was different from both, and my 1960's learning had moved on again. In 1933 much attention paid to heat (steam), and optics (fresnel lighthouses), but no mention of atomic structure. 1960's no mention of steam engines, or light-houses, large chunks of old-fashioned chemical analysis had disappeared, replaced by orbitals, electrons, and physical chemistry. My children's textbooks were different again. The underlying science is much the same, but the emphasis is different. All that effort I put into learning how to make coal-gas and recover a multitude of useful organic chemicals by roasting coals was wasted! No surprise that the language we use varies over time. Best not to die in a ditch over it!

Choo-choos process is aimed at small workshops. It's conveniently easy rather than top-notch, producing an unpredictably thin hard layer. No box needed because it relies on a source of clean heat such as a blowlamp, and melting chemicals in the mix keep air out for long enough to get a reasonable result. Not to be compared with industrial hardening, where a thick layer of known depth is required, and the finished item has to meet a hardness specification. Choo-choo's mild-steel screwdriver will perform better after simple hardening, but it won't be anything like as hard wearing as a commercial screwdriver. An excellent learning opportunity rather than the best of all possible ways to make a screwdriver!

Dave

[FulmenParticipant @fulmen]

The way I understand "case hardening" describes any process where a hard outer "case" is applied to a part. The classic process is as Bill Davies said "pack carburizing" where carbon is added to low carbon steel by heating it in a closed box with charcoal. Other processes adds nitrogen (nitriding) or a combination of carbon and nitrogen ( carbonitriding) using either a molten salt bath or a controlled gas atmosphere.

A simple yet effective concoction is regular BBQ charcoal with say 5% of calcium carbonate (limestone) and/or sodium carbonate (washing soda). The carbonates provides a source for CO2 which combined with the charcoal forms carbon monoxide. This is the actual carrier that transports carbon into the part.

The deposition rate is slow. You can expect a case depth of 0,1mm per hour at the beginning, but this quickly drops as case depth increases.

[duncan webster 1Participant @duncanwebster1]

That's the first time I've seen the OED quoted as an authority on metallurgy. SOD's reference might well have been the only way in ancient times, (they also used bone dust, a byproduct of making buttons) but for a long time Fulmen's definition is correct

[FulmenParticipant @fulmen]

@SillyOldDuffer: Various carbonates are added as "activators", but I haven't found any good info on the reason for the different metals used. But I suspect it has to do with the temperature and rate of decomposition (into CO2 and the corresponding metal oxide). Barium carbonate breaks down more slowly than sodium or calcium carbonate so I suspect it's mostly needed for very thick casings on large parts. These can take days to form.

I actually have suitable barium salts, but never tried it due to it's toxicity. In my experience a 50/50 mix of sodium and calcium carbonate will work just fine.

IIRC Cherry Red was primarily ferrocyanides, forming a very thin nitrocarburizing case. While nitrides provide a very hard, wear resistant case they don't really provide the increased structural strength that carburizing does.

[Clive HartlandParticipant @clivehartland94829]

While working the plating shop as part of my training there was a process called Black Chrome.The parts were first Copper plated and immersed in what looked like boiling sawdust mixture. Upon removing the parts were then brushed to get the copper plating off, and up came a lustrious black chrome. I later learnt that Browning shotguns had black chrome barrels to prevent wear.

The application I saw was for the internal parts of large gun recuporators.

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